A fuel cell includes unit cells that can produce electrical energy through an electrochemical reaction of hydrogen and oxygen. The fuel cell is designed to have bipolar plates attached to both surfaces of a membrane electrode assembly (MEA), respectively. A bipolar plate includes a gas channel supplying reactant gases such as hydrogen and oxygen to the MEA and a cooling channel allowing a coolant to circulate.
The amount of water distributed in the MEA is generally increased from an upstream part to a downstream part of the gas channel of the bipolar plate. Thus, the MEA becomes dry in the upstream part of the gas channel, and becomes wet in the downstream part of the gas channel.
When the MEA becomes dry or wet compared to an appropriate level of humidity, the speed of the reactant gases passing through the MEA may be decreased, and thus performance of the fuel cell may be degraded and an electrolyte membrane of the MEA may be damaged to cause a reduction in durability. Therefore, in order to improve the performance and durability of the fuel cell, an appropriate amount of water should be distributed uniformly over an entire region of the MEA. However, a conventional fuel cell involves a problem in that it is not designed to uniformly distribute the appropriate amount of water to the MEA.
Further, the gas channel of the bipolar plate may be designed to decrease resistance near a supply manifold and an exhaust manifold for smooth supply and exhaust of the reactant gases. However, a conventional fuel cell involves a problem in that it is not designed to easily adjust resistance in the channels of the bipolar plate according to regions of the bipolar plate.